Burden of disease due to human coronavirus NL63 infections and periodicity of infection

BACKGROUND: The disease burden caused by recently identified respiratory viruses like HCoV-NL63 is unknown. OBJECTIVES: We determined the burden of disease due to HCoV-NL63 infections using the population-based PRI.DE cohort of children under the age of 3 with lower respiratory tract infections (LRTIs). STUDY DESIGN: In total 1756 respiratory samples, from hospitalized children or children who visited the outpatient clinic, were tested for HCoV-NL63. Sampling covered a period of 2 years and the frequency of infection in different years was compared to other Western European studies that tested for this virus in 2 or more consecutive years. RESULTS: Sixty-nine samples were HCoV-NL63 positive, 35 were with high loads, and of these 25 were single HCoV-NL63 infections. Based on the number of children with high HCoV-NL63 infection and no additional infection, the overall annual incidence in outpatients was 7 per 1000 children per year (95% confidence interval (CI) 3–13 per 1000 children per year), which can be extrapolated to an absolute number of 16,929 visits to the physician due to an HCoV-NL63 infection in Germany per year. The estimated hospitalization rate is 22 per 100,000 children (95% CI: 7–49 per 100,000 children per year). This number reflects 522 HCoV-NL63 children in Germany per year. A large year-to-year difference in HCoV-NL63 infection frequency was observed. Combining these data with those of other studies in Western Europe revealed that HCoV-NL63 infections follow a 2-year inter-epidemic period with peaks of infection in the winters of 2000/2001, 2002/2003 and 2004/2005 (p < 0.0001). CONCLUSIONS: HCoV-NL63 infection in children below 3 years of age often requires a visit to the physician in an outpatient clinic, especially during peak-years, but hospitalizations are relatively infrequent.